But despite armed police dealing with the incident in a basement under the ministerial corridor, the incident did not create a larger emergency on the Parliamentary estate.

Other buildings were not on lockdown and visitor tours were allowed to continue while officers dealt with the situation.

A statement from the Met police said: “At approximately 11.36am on Tuesday, 13 February, police were informed of a suspicious package that had been delivered to an office within the Palace of Westminster. Police are at the scene and dealing.”

Reuters

The powder was reportedly sent to Amber Rudd, though the Home Secretary is currently in America

They added: “The letter contained a white powder which is currently being assessed by specialists. The office remains closed at this time, but the rest of the Palace of Westminster is open.

“Detectives from the Met’s Counter Terrorism Command have been informed and are investigating.”

The Sun understands it was sent to Cabinet minister Ms Rudd's office, with staff being forced to evacuate and the authorities alerted.

A source said: "Police and security were all over the Home Secretary’s staff office, they threw us all out in panic and suddenly coppers were everywhere."

PA

Specialist officers are reportedly dealing with the incident in Parliament

A House of Commons Spokesperson says: “Today the Metropolitan Police investigated a small package containing white powder on the Parliamentary Estate.

“The powder was found to be non-harmful.”

No extra officers were visible at the main entrance at Carriage Gates today, but there was a security message being displayed on the screens in some of the buildings.

It says: "Incident in the house of Commons being dealt with by the Metropolitan Police. Do not be alarmed."

UPDATE: The white powder has been assessed by specialists and found not to be noxious. The office remains closed at this time, but the rest of the Palace of Westminster is open

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Witnesses had earlier said police had told them they were dealing with a “suspicious package”, which was confirmed by an unnamed officer.

He said: "We haven't been told much, but a package has been left. Specialist officers have just arrived to examine it. It won't be anything to worry about."

Most MPs are not in Westminster this week as Parliament is in recess for school half-term.

Police have increased security at parliament after an Islamic State-inspired attacker killed five people a year ago by driving a car into pedestrians on Westminster Bridge and then stabbing to death a police officer in the grounds of Parliament.

Home Secretary Amber Rudd says Britain will 'absolutely grow' after Brexit depending on the actions we take